Device for reading out exposed imaging plates

ABSTRACT

A device for reading out and erasing imaging plates which includes an eraser disposed down-stream of a readout unit at a short distance thereof, said eraser being separated from the readout unit by a light barrier.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/992,615 filed on Mar. 26, 2008, which claims the filing benefit ofPCT Patent Application No. PCT/EP2006/008262, filed Aug. 23, 2006; whichclaims the benefit of German Patent Application No. 10 2005 046 249.9,filed Sep. 27, 2005; the contents of all of which are incorporatedherein by reference.

TECHNICAL FIELD

The invention relates to a device for reading out exposed imagingplates, according to the precharacterising portion of a device forreading out exposed imaging plates, with retaining means for retainingin given geometry an imaging plate to be read out, with a reading unitwhich generates a reading light beam which is moved in a first scanningdirection and exhibits detection means for detecting fluorescent lightreleased in the imaging plate by the reading beam, and with a drivedevice for generating a relative motion between the imaging plate andthe reading unit in a second scanning direction, different from thefirst scanning direction, wherein an erasing unit is arranged in thedirection of the second scanning direction behind the reading unit andaligned with the latter, in that the drive device is designed in such away that it also extends over the erasing unit, and in that a lightbarrier is arranged between the reading unit and the erasing unit.

BACKGROUND OF THE INVENTION

Exposed imaging plates contain a latent X-ray image, in the form oflocally excited metastable excited states of colour centres, which isobtained by the imaging plate being placed behind an object in X-raylight generated by an X-ray source.

This latent image is read out by the imaging plate being scanned, pointby point, with a readout beam of small diameter. The wavelength of thereadout light is chosen in such a way that it excites a metastableexcited centre into a higher electron state which rapidly decays,accompanied by fluorescence.

The fluorescent light emitted in such a way is measured with a detectiondevice which, for example, may contain a photomultiplier by way oflight-sensitive element. From the electrical output signal of thedetection means and from electrical signals that reproduce theinstantaneous position of the readout beam, an image of the transmissionof the object, expressed by electrical signals, can then be obtained.

An advantage of the imaging plates in comparison with conventional X-rayfilms is the fact that the imaging plates can often be used again. Sincein the course of the readout procedure some of the excited electronstates of the centres remain behind by reason of the only brief localexposure by the readout beam, it is necessary to erase the imaging platereliably before a new recording by irradiating it intensely and for arelatively long time with erasing light. If this is not done, a shadowof the preceding X-ray image may appear on the next X-ray image.

The erasing devices that have been used hitherto for imaging plates areseparate instruments, into which the imaging plates are passed when theyhave left the readout device. With regard to the high costs of theimaging plates and the large number of radiographs that are taken inhospitals and similar institutions, it is advantageous if an imagingplate is available again as quickly as possible after the latent imagehas been read out.

The present invention is directed to addressing these and other matters.

SUMMARY OF THE INVENTION

For the purpose of achieving this object, by means of the presentinvention a device for reading out exposed imaging plates is specifiedwith which the erasing of remnants of the latent image which remainafter the readout is effected substantially synchronously with thereadout. The device for reading out exposed imaging plates havingretaining means for retaining in given geometry an imaging plate to beread out, with a reading unit which generates a reading light beam whichis moved in a first scanning direction and exhibits detection means fordetecting fluorescent light released in the imaging plate by the readingbeam, and with a drive device for generating a relative motion betweenthe imaging plate and the reading unit in a second scanning direction,different from the first scanning direction, an erasing unit is arrangedin the direction of the second scanning direction behind the readingunit and aligned with the latter, in that the drive device is designedin such a way that it also extends over the erasing unit, and in that alight barrier is arranged between the reading unit and the erasing unit.

With the further development of the invention including a light-sourcethat exhibits a bundle of erasing-light-absorbing lamellae which arearranged in parallel, with a spacing, the edges of which pointingtowards the imaging plate are spaced from the trajectory of the imagingplate. With such a light source, it is ensured that, with a smalldimension of the light barrier in the conveying direction of the imagingplate, a very reliable partitioning of the light to the reading head isobtained. Such small dimensions in the conveying direction of theimaging plates are therefore of interest, since in this way the erasinghead can be provided very close to the reading head. By this means, thetime that is needed overall in the device for the readout and erasurebecomes only insignificantly longer in comparison with the time-intervalthat is needed for the readout of the imaging plate alone.

In the course of the erasing of remnants of the latent image,fluorescent light also arises at the erasing head. With the furtherdevelopment of the invention providing that the lamellae also absorbfluorescent light which guarantees that not only no erasing light butalso no fluorescent light gets from the region of the erasing head intothe region of the reading head where, as a result, the readout ofsubsequent image regions could be disturbed.

In the case of a light barrier, the clearance between the edges of atleast some of the lamellae facing towards the imaging plate amounts toabout 0.05 mm to about 0.2 mm which are thin absorbent chambers whichextend away from the conveying face of the imaging plate and the freeedges of the lamellae pointing towards the imaging plate small, so thatonly few reflections are obtained there.

With the further development of the invention including the edges of atleast some of the lamellae facing towards the trajectory of the imagingplate are sharpened in order to ensure that a reflection on the freeedges of the lamellae is again reduced.

With the further development of the invention including a light barrierwherein the lamellae are spaced by intermediate second lamellae, theedges of which facing towards the imaging plate exhibit greater spacingfrom the imaging plate than the corresponding edges of the firstlamellae. This can be produced very easily by forming a stack consistingof two different types of lamella.

With the further development of the invention providing that the spacingbetween the free edges of the second lamellae and the trajectory of theimaging plate amounts to at least 10 times the spacing between the freeedges of the first lamellae and the trajectory of the imaging plateguaranteeing that, even when the absorbently configured surfaces—forexample, surfaces covered with black lacquer—of the lamellae stillreflect some light, a good absorption is guaranteed overall by virtue ofthe depth of the flat pockets situated between the lamellae.

In the case of a light barrier that is designed in a manner where thesecond lamellae exhibit interruptions which are connected to acooling-gas distributor space, a cooling gas can be supplied to the flatpockets situated between the lamellae, and in this way the heat arisingin the course of the absorption of light can be dissipated well. In thisway, contaminants such as dust, which in the course of time could formcentres for the reflection of light, are also prevented from beingdeposited in these flat pockets.

With the further development of the invention providing that thelamellae exhibit regions pressed out of their plane, via which they arespaced meaning a lamellar stack can be produced by using only one typeof lamella in very simple manner.

The peripheral direction the lamellae are provided symmetrically withregions pressed out of their plane, and the pressed-out regions ofadjacent lamellae are offset in relation to one another guaranteeingthat the lamellae do not tilt against one another and are stacked onebehind the other in very producible and reliable manner.

The further development of the invention providing that the peripheralsurface of the lamellar bundle are connected to a distributor space forcooling gas which is advantageous with regard to good dissipation ofheat from the light barrier.

The further development of the invention including a light barrier thatincludes a pile made of absorbent textile material which will satisfythe requirements for many cases. It can be produced particularlyinexpensively and simply.

With the further development of the light barrier including a pileincludes that the pile is a pile-loop fluorine, it is ensured that whenthe fluorine of the light barrier is arranged particularly close to thetrajectory of the imaging plates any chance contacts of the ends of thefluorine loops do not leave scratches behind on the surface of theplate.

The further development of the light barrier including a pile whereinthe pile is produced from a material that absorbs in volume which isadvantageous with regard to absorption of erasing light and fluorescentlight that is as complete as possible.

If the individual fluorine fibres contained in the pile of thelight-barrier are treated so that the absorbent material is frosted onits outside, residual reflections on the fibre surface are largelyeliminated.

The same holds for fibrous material having the outer surface of thetextile material studded with absorbent particles.

A further development of the invention includes an erasing-light sourceincluding a fluorescent lamp, which is distinguished by little evolutionof heat.

A still further development of the invention includes an erasing-lightsource that includes a plurality of light-emitting diodes which arespaced in such a manner that their light cones overlap in the surface ofthe plate, which is distinguished by low energy consumption and compactdimensions, as well as long life.

Still further developments include light-emitting diodes that arearranged in several rows spaced in the conveying direction of theimaging plate, wherein the diodes of consecutive rows are offset inrelation to one another, and the light-emitting diodes are arranged on acarrying body that is driven in the direction perpendicular to theconveying direction of the imaging plates, which guarantees a uniformerasure of the imaging plate.

These and other objects and advantages will be made apparent from thefollowing brief description of the drawings and the detailed descriptionof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: shows a schematic lateral view of a combined device for readingout and simultaneously erasing the light-sensitive layer of an imagingplate;

FIG. 2: shows an axial section through a light barrier which is arrangedbetween the erasing head and the reading head of the combined deviceaccording to FIG. 1;

FIG. 3: shows an enlarged top view of a first type of ring lamella,which is used in constructing the light barrier according to FIG. 2;

FIG. 4: shows a top view of a second circular type of lamella, which isused in constructing the light barrier according to FIG. 2;

FIG. 5: shows a top view of another modified type of a circular lamellafrom which a stack of spaced shielding lamellae can be produced;

FIG. 6: shows an axial section through a modified light barrier;

FIG. 7: shows a transverse section through an absorbent textile thread;

FIG. 8: shows a lateral, partly sectional, view of an LED erasing-lightsource and of a drive for said source; and

FIG. 9: shows a lateral view of a modified readout device of theflatbed-scanner type.

DETAILED DESCRIPTION OF THE INVENTION

While this invention is susceptible of embodiment in many differentforms, there is shown in the drawings and will herein be described indetail one or more embodiments with the understanding that the presentdisclosure is to be considered as an exemplification of the principlesof the invention and is not intended to limit the invention to theembodiments illustrated.

A combined device for reading out and erasing exposed imaging plates isdenoted overall by 10 in FIG. 1. It consists of a readout unit, denotedoverall by 12, and an erasing unit, denoted overall by 14.

The readout unit 12 includes a mounting table 16 which exhibitscylindrical shape and three belt conveyors 18 distributed around theperiphery of the mounting table, which are coupled to one anothermechanically and connected to the output shaft of an electric motor 20.The electric motor 20 is, in turn, connected to a position indicator 22.The latter provides its output signal on a line 24.

The mounting table 16 has an annular gap 26 extending in the peripheraldirection, through which a peripheral reading beam 28 emerges. It is aquestion of laser light with a wavelength that is suitable for furtherexcitation of a metastably excited centre of an imaging plate. Withrespect to particulars of the reading head, reference is made to WO01/18796 A1, the content of which is hereby also to be made part of thepresent application.

Indicated by 30 in the drawing is an exposed imaging plate which isarranged with its light-sensitive layer downward on the mounting table16. It is held in cylindrical geometry by the three belt conveyors 18which are distributed in the peripheral direction. At the same time, thebelt conveyors 18 move the imaging plate 30 in FIG. 1 to the right andacross the annular gap 26. In the process, the image-points of thelatent image that are situated precisely above the annular gap are readout by the peripheral light beam 28.

The readout unit 12 receives, via a line 32, an operating voltage forsupplying the various loads contained in it and emits, via a line 34, anelectrical signal corresponding to the instantaneous angular position ofthe reading beam 28, and, via a line 36, the output signal of aphotomultiplier contained in it.

The position indicator 22 coupled with the electric motor 20 emits anoutput signal that corresponds to the position of the imaging plate 30with respect to the annular gap 26.

From the electrical signals applied to the lines 24, 34 and 36 it isthen possible for the electronic image of the latent X-ray image to begenerated, as described in detail in WO 01/19796 A1.

The erasing unit 14 has a broad transparent exit window 40 for erasinglight, extending in the peripheral direction, the external face of whichconstitutes a smooth continuation of a mounting table 42. Distributedaround the mounting table 42 are belt conveyors 44 which aremechanically coupled with one another and with the belt conveyors 18.

From the annular exit window 40 an annular curtain of erasing lightemerges. Since the erasing light acts simultaneously on all the pointsof the imaging plate situated on a scan line in the peripheraldirection, simply by reason of the time-factor (ratio of pixel to scanline) a stronger illumination obtains in the erasing unit 14 than abovethe annular gap 26 of the reading unit. Furthermore, the erasing lightcan also be chosen to be more broadband, and can be generated by anon-coherent light-source.

The fluorescent lamp 48 may be a warm-tone tubular fluorescent lamp.With such lamps an illuminance of 50,000 1x can be obtained. For thepurpose of erasing an imaging plate, a quantity of light ofapproximately 500,000 1x s is needed if it is desired to obtain theerasure within a short time synchronously with the readout of theimaging plate.

If readout and erasure take place in a combined readout-and-erase devicewith a common transport device which moves the imaging plates throughthe reading unit and the erasing unit, then the erasing-time issubstantially the readout-time plus the time that is needed for bridgingthe spacing between the reading unit and the erasing unit.

The time for reading out an imaging plate results from the afterglowduration of the storage phosphor. If the light-sensitive layer of animaging plate contains a BaFBr:Eu material by way of storage phosphor,then the afterglow duration after irradiating with the laser light thatis used for readout amounts to 880 ns. From this, a readout duration ofan order of magnitude of 10 s results for imaging plates for intra-oralapplication.

Tubular fluorescent lamps are suitable as sources of light for theerasing unit 14 also for the reason that they exhibit a high energyefficiency. A further advantageous aspect of such lamps is that theyheat up only a little, so that the imaging plates are not damaged by theaction of heat in the course of erasure.

In order not to exclude components in the spectrum of the fluorescentlamp 48 that are useful for the erasing, a plastic film which operatesas an optical cut-off filter may be arranged around said lamp. This isselected in such a way that only lets through the spectral componentsthat are desirable for the purpose of erasing, with wavelengths above480 nm.

In the exemplary embodiment being considered here, instead of such aplastic film the exit window 40 is produced from a transparent materialthat exhibits appropriate filter characteristics.

Such a cut-off filter is also advantageous with regard to an additionallight barrier between the erasing unit and the reading unit, since ablue filter for fluorescent light, which only lets through wavelengthsbelow approximately 450 nm, is arranged upstream of the photodetector ofthe reading unit. This blue filter blocks off the erasing light.

A perfect erasure when reading out storage centres that have not yetbeen deactivated is also guaranteed, for the reason that the axialdimension of the exit window 40 is distinctly greater than that of theannular gap 26 or the diameter of the readout beam 28.

In practice, for the stated reasons, axial dimensions of the exit window40 that are about 20 to 100 times greater than those of the annular gap26 are entirely sufficient.

In the course of moving across the exit window 40, the storage centresthat have not yet been deactivated in the course of readout areconsequently erased, and if the imaging plate 30 has then passed overthe exit window 40 completely it can be used directly for a new X-rayexposure.

In order to prevent erasing light emerging through the exit window 40(and fluorescent light arising in the course of erasing) from gettingback to the reading unit 12, where they could disturb the readout ofsubsequent image regions, an annular light barrier 46 is providedbetween the reading unit 12 and the erasing unit 14.

For the sake of greater ease of representation, in the drawing the lightbarrier 46 has been represented with dimensions in the conveyingdirection of the imaging plate that are distinctly increased incomparison with practical application. In practical exemplaryembodiments the light barrier 46 will be chosen to be precisely so longas necessary in the plate-conveying direction with regard to adequateeffectiveness of the light barrier.

The closer the exit window 40 can be shifted towards the annular gap 26,the less does the total time needed for the readout and erasing differfrom the time that is needed for pure readout.

FIG. 2 shows a practical exemplary embodiment of an erasing device withupstream light barrier.

Behind the exit window 44, which takes the form of an annular glass orplastic body, an annular fluorescent lamp 48 is located. Behind this atoroidal parabolic mirror 50 is located which is constituted by thefrosted surface of a rotationally symmetrical mirror body 52. The latteris inserted flush into the interior of the ends of the mounting tables16 and 39 of the readout unit 12 and the erasing unit 14, respectively.

The light barrier 46 has a housing 54 which surrounds a cylindricallamellar bundle 56, subject to radial clearance, so that outside thelamellar bundle an annular space 58 is obtained which is connected to acooling-gas feed line 60.

The lamellar bundle 56 consists of first lamellar discs 62 and secondlamellar discs 64 stacked alongside one another in alternating manner.These discs have the same outside diameter but greatly differing insidediameters, so that axially flat annular pockets 66 between the lamellae62 and 64 are obtained, the radial extent of which is large incomparison with their axial dimension.

The lamellar discs 62, 64 are lacquered black or provided in some otherway with a surface that absorbs erasing light emitted from thefluorescent lamp 48, and preferably also fluorescent light.

The two types of lamellar discs 62 and 64 are shown in more detail inFIG. 3.

The lamellar discs exhibiting small radial width are in each instanceinterrupted at a point on their periphery, as shown at 68. In this way,cooling gas is able to flow from the bottom of the pockets 66 to theiropen end when cooling gas is applied to the annular space 58.

The light barrier 46 operates in such a way that it absorbs lightreflected from the surface of the mounting table 16, or light reflectedfrom an imaging plate.

But a certain residual reflection is also characteristic of surfacesthat have been dyed black or dyed otherwise so as to be light-absorbing.For this reason, the surfaces situated radially on the inside of thering openings are kept small by virtue of the fact that only very smallaxial dimension is given to the first lamellar discs 62. Typically theselamellae may have been produced from a material similar to that ofrazor-blades—that is to say, they have a thickness of only 0.1 mm.

In order to reduce the size of the front faces further, the internaledges of the lamellar discs 62 can be sharpened like knife-edges, asindicated at 70 in FIG. 3, with the angled side of the sharpening 70 inthe disc stack pointing towards the erasing unit 14.

Alternatively, the lamellar bundle 56 may also be exhibited fromlamellar discs of the same type if the latter are provided withprotruding sections as shown in FIG. 5. Therein, in a lamellar disc 62as also already shown in FIG. 3, circular regions 72 have been pressedout axially.

These pressed-out regions may also have larger axial dimensions than thethickness of the lamellar disc 62, so that pockets 66 exhibiting greateraxial dimension are obtained. But, as in the case of the exemplaryembodiment according to FIG. 4, in which the lamellar discs 62 and 64were of equal thickness, the axial dimension of the pressed-out circularregions 72 may also be chosen to be substantially the same size as thethickness of the lamellar disc 62, and a lamellar bundle 56 is thenobtained as shown in FIG. 2, with the single difference that the pockets66, apart from small peripheral interruptions, are continuouslyconnected to the annular space 58. By this means, a cooling of all thelamellar discs is obtained that is highly uniform in the peripheraldirection.

It will be understood that the lamellar discs according to FIG. 5 arestacked one behind the other for the purpose of forming the lamellarbundle 56 in such a way that their pressed-out regions 72 are offset inrelation to one another by 45°.

If desired, a light barrier of the type described above may also beprovided on the inside of the mounting table 16, as indicated by adashed line at 74.

The radial position of the inner edges of the lamellar discs 62 (andcorrespondingly the radii of the external edges of similar lamellardiscs in a light barrier 74) is chosen in such a way that, on the onehand, they are situated as close as possible to the outside of animaging plate 30 being moved past and, on the other hand, a directcontact is certainly avoided.

In practice, the spacings between the inner edges of the lamellar discs62 (or of the outer edges of lamellar discs of a light barrier 74) mayexhibit a spacing of 0.1 mm to 0.5 mm from the adjacent surface of theimaging plate 30. In this way, the light barrier 44 operates incontact-free manner and nevertheless ensures, by virtue of the deepabsorbent pockets 66, that no light gets from the erasing unit 14 to thereading unit 12.

As an alternative to a light barrier 46 with a lamellar bundle 56 asdescribed above, use may also be made of a light barrier 46 according toFIG. 6, the manufacturing costs of which are low.

A layer of a pile-loop fabric 76 has been directly applied onto theinside of the sheath-shaped housing 54. Said fabric consists of a fabriclayer 78 and a plurality of pile loops 80 bearing said layer.

The height of the pile loops 80 is chosen in such a way that theyexhibit only small spacing from the adjacent upper side of an imagingplate being moved past.

Since the pile loops 80 are closed, they do not have any sharp edgesthat have arisen as a result of cutting away fibres and that, with animaging plate frequently running past, could generate scratch marks orstress marks on said imaging plate.

As is evident from the drawing, the pile loops 80 are set closelytogether so that they stabilise one another against the influence ofgravity. The pile loops consequently remain substantially radiallyaligned over the entire periphery of the inner surface of the housing54.

The pile loops 80 are produced from a flexible material which ispigmented in volume. In this connection, in particular fine carbon-blackand black plastic dust—as used in toner powders, for example—enter intoconsideration as pigments.

In order once again to avoid reflections on the fibre surface, thelatter is frosted, it being possible for this to be effected in a mannerknown as such in the finishing of plastic films by chemical etching orby treating in a gas discharge.

Alternatively, as shown in FIG. 7, for the purpose of producing the pileloops use may also be made of a thread material 82 that exhibits athermoplastic core and black absorber particles 86 firmly weldedthereon. Such a thread material can be produced, for example, by drawingit through a hot powder bed consisting of the absorber particles and,after this treatment, by blowing off absorber particles 86 that are notfirmly bonded.

Instead of the fluorescent lamp 48, use may also be made of otherlight-sources, the light of which exhibits a minor component in the blueand in the UV, for example a fluorescent lamp, the glass tube of whichis coated with a red phosphor.

In order to be able to realise still shorter erasing-times, a halogentorch may also be employed. The latter has a higher power consumptionand a higher light-emission intensity, relative to the area of theemitter (incandescent filament).

The walls of the erasing unit 14 surrounding the light-source arepreferably coated with a material reflecting very well in respect of theerasing light, which reflects diffusely. Well suited, for example, arewhite or yellow foam material, white Teflon and brightly polishedaluminium sheet. A particularly good reflection layer consists of aBaSO₄ material, in particular such a material that has been mixed with ayellow dyestuff. Any wall material can then be coated with thismaterial.

However, in addition to the conventional light-sources mentioned above,solid-state light-sources (LEDs) are also suitable for erasing theimaging plates. These sources are currently only available as discreteindividual elements with relatively small dimensions. In order to fillout the entire annular exit window 40 with an annular light curtain,instead of the fluorescent lamp 48 use is made of an annular LEDlight-source 48′ as shown in FIG. 8.

On the outside of a carrying ring 88 there are arranged, regularlydistributed in the peripheral direction, light-emitting diodes 90, theoperating wavelength of which lies above 480 nm (typically around 630nm), so that their light is suitable for erasing purposes but thereadout of the imaging plate is not disadvantageously impaired.

With regard to the uniformity of illumination of the exit window,preferably two axially spaced rings of light-emitting diodes 90 areprovided, in which the individual light-emitting diodes are offset inrelation to one another by half a pitch.

It will be understood that the light-emitting diodes are situated at anappropriate distance behind the exit window 40 in such a manner that thelight cones emitted from them just overlap on the outer surface of theexit window 40.

For the purpose of still further homogenisation of the illumination ofthe exit window 40, the exit window 40 may be frosted, and/or thecarrying ring 88 may also be provided with an internal gearing and maybe rotated via a pinion 92, so that residual ripples in the intensitydistribution in the peripheral direction fall out as a result oftemporal averaging. Hence a homogeneously good erasure of the imagingplate 30 when passing through the erasing unit 14 is guaranteed.

If imaging plates of greatly differing dimensions are erased in theerasing unit 14, the light-emitting diodes 90 may be subdivided intogroups also in the peripheral direction, and, for the purpose oferasing, only those groups may be activated in each instance whichtogether cover the width of the imaging plate 10.

For the purpose of improving the dissipation of heat, the carrying ring88, like the light-emitting diodes 90, may be produced from materialthat conducts heat well, for example aluminium. Where appropriate, thecarrying ring 88 may also be cooled by being subjected to incident flowof air, or by means of a liquid coolant circulated in an internalcoolant channel.

If the scanner is a flat-picture scanner, then a shielding (whereappropriate, also in addition to the shielding measures described above)of the readout unit 12 against erasing light may be brought about by theimaging plate being guided in front of the reading unit in planes thatare spaced from one another and preferably parallel to one another.

An exemplary embodiment of such a type is shown in FIG. 9. Parts of thereadout and erasing device that correspond, from the viewpoint offunction, to those in the exemplary embodiments described above areagain provided with the same reference symbols and do not need to bedescribed again in detail below.

The readout and erasing device 10 shown in FIG. 9 takes the form of aflat-picture scanner. The imaging plate 30 is consequently moved throughthe readout unit 12 in a flat configuration.

Behind the readout unit 12 three rollers 96, 98, 100 are now providedwhich deflect the imaging plate 30 out of a first conveying plane F1,which applies in the case of the readout unit 12, into a second parallelconveying plane F2 spaced upwards, which applies in the case of theerasing unit 14.

By virtue of this step in the conveying path, the danger is that erasinglight emitted from the erasing unit 14, which reaches the environment onleakage thread, does not reach the readout unit 12. If the rollers 96 to100 extend over the entire width of the imaging plate 30, the rollers96, 98, 100 furthermore constitute additional screens partitioning thelight, which engage the imaging plate 30 in practically spacing-freemanner.

It is known that both broadband erasing-light sources such asfluorescent lamps, halogen lamps or xenon lamps are subject to an ageingprocess by which the emitted quantity of light is reduced. Also in thecase of narrowband erasing-light sources, such as LEDs, there is adecline in the emitted luminous flux, which is associated withincreasing operating-time.

In order to counter this, as likewise shown in FIG. 9, in the erasingunit 14 a photodiode 102 or another light-sensitive element may beprovided, the output signal of which changes in accordance with thechange in the luminous flux generated by the lamp. The output signal ofthe photodiode 102 can then be used either to increase the operatingcurrent of the light-source in such a way that the emitted luminous fluxremains unchanged, or to reduce the conveying speed of the imaging plate30 in the region of the erasing unit 14 in such a way that the sameradiation dose is obtained even with reduced luminous flux.

In the case where use is made of a narrowband erasing-light source, thepeak wavelengths can be adapted to the peak wavelength of the absorptionof the F-centres of the phosphor material in order to obtain aparticularly efficient erasing of remaining image residues.

In further modification of the exemplary embodiments described above, byusing optical elements (mirrors, lenses) the angular range of theerasing lamp can be restricted to those spatial regions in which theimaging plate runs past in front of the erasing unit. In this way, anincrease in the intensity of the erasing light is obtained, andcorrespondingly the possibility of a shortening of the erasing-time.

The invention claimed is:
 1. A device for reading out exposed imagingplates comprising: retaining means for retaining in given geometry animaging plate to be read out, a reading unit which generates a readinglight beam which is moved in a first scanning direction and exhibitsdetection means for detecting fluorescent light released in the imagingplate by the reading beam, and a drive device for generating a relativemotion between the imaging plate and the reading unit in a secondscanning direction, different from the first scanning direction, whereinan erasing unit is arranged in the direction of the second scanningdirection behind the reading unit and aligned with the latter, in thatthe drive device is designed in such a way that it also extends over theerasing unit, and wherein a first portion of the imaging plate is erasedat the same time a second portion of the imaging plate, different thanthe first portion, is read, and wherein a light barrier is arrangedbetween the reading unit and the erasing unit, and wherein the lightbarrier comprises a guidance unit which predetermines a step in aconveying path of the imaging plate such that the plate is deflected bythe guidance unit.
 2. The device of claim 1, wherein the light barrierfurther comprises a plurality of erasing-light-absorbing lamellae whichare arranged in parallel, with a spacing, the edges of which pointingtowards the imaging plate are spaced from the trajectory of the imagingplate.
 3. The device of claim 2, wherein the lamellae absorb fluorescentlight.
 4. The device of claim 2, wherein the clearance between the edgesof at least some of the lamellae facing towards the imaging plateamounts to about 0.05 mm to about 0.2 mm.
 5. The device of claim 2,wherein the edges of at least some of the lamellae facing towards thetrajectory of the imaging plate are sharpened.
 6. The device of claim 2,wherein the lamellae are spaced by intermediate second lamellae, theedges of which facing towards the imaging plate exhibit greater spacingfrom the imaging plate than the corresponding edges of the lamellae. 7.The device of claim 6, wherein the spacing between the free edges of thesecond lamellae and the trajectory of the imaging plate amounts to atleast 10 times the spacing between the free edges of the first lamellaeand the trajectory of the imaging plate.
 8. The device of claim 6,wherein the second lamellae include interruptions which are connected toa cooling-gas distributor space.
 9. The device of claim 8, wherein theperipheral surface of the lamellar bundle are connected to a distributorspace for cooling gas.
 10. The device of claim 2, wherein the lamellaeinclude regions pressed out of their plane, via which they are spaced.11. The device of claim 10, wherein in the peripheral direction thelamellae are provided symmetrically with regions pressed out of theirplane, and the pressed-out regions of adjacent lamellae are offset inrelation to one another.
 12. The device of claim 1, wherein the lightbarrier includes a pile made of absorbent textile material.
 13. Thedevice of claim 12, wherein the pile includes fluorine fibers.
 14. Thedevice of claim 12, wherein the absorbent textile material is frosted onits outside.
 15. The device of claim 12, wherein an outer surface of theabsorbent textile material is studded with absorbent particles.
 16. Thedevice of claim 1, further comprising a light-source of the erasing unitincluding a fluorescent lamp.
 17. The device of claim 16, wherein aspectrum of the light source is set to a maximum of an absorption ofstorage centres of the imaging plate.
 18. The device of claim 16,wherein the walls of the erasing unit surrounding the erasing-lightsource are designed to be diffusely reflecting.
 19. The device of claim16, wherein the walls of the erasing unit surrounding the erasing-lightare provided with a coating that reflects erasing light.
 20. The deviceof claim 1, further comprising a light-source of the erasing unitincluding a plurality of light-emitting diodes which are spaced in sucha manner that their light cones overlap in the surface of the plate. 21.The device of claim 20, wherein the light-emitting diodes are arrangedin several rows spaced in the conveying direction of the imaging plate,and the diodes of consecutive rows are offset in relation to oneanother.
 22. The device of claim 20, wherein the light-emitting diodesare arranged on a carrying body which is driven in the directionperpendicular to the conveying direction of the imaging plates.
 23. Thedevice of claim 1, further comprising a light-sensitive element whichhas erasing light applied to it.
 24. The device of claim 23, furthercomprising a device for regulating the luminous flux emitted by a sourceof the erasing light, which operates as a function of the output signalof the light-sensitive element which has erasing light applied to it.25. The device of claim 1, further comprising a means for collectingerasing light emitted by the erasing unit onto that spatial region inwhich an imaging plate is moved past the erasing unit.